Service tax date issue for march bill and manpower supply

GAURANG KACHHIA (ACCOUNT EXECUTIVE) (41 Points)

04 April 2015  
as we are following mercantile accounting system . I want to know if a manpower agency send a bill for manpower supply for the month march 15 to a corporate entity, so on which date i should issue invoice on 31st march2015 or after 31st march 2015. because client demanding invoice dated after 31st march 2015. i.e invoice date on or after 01/04/2015 so in that case what will be our liability regarding the ST liability.????
as the there is amendments in the notifiaction w.e.f. 01/04/2015 the liability of paying S.T. is 100% on service receiver if service receiver is coporate entity.